Cesium 137’s half-life — the time it takes for half of a given amount of material to decay — is 30 years. In addition to that, cesium-137’s total ecological half-life — the time for half the cesium to disappear from the local environment through processes such as migration, weathering, and removal by organisms is also typically 30 years or less, but the amount of cesium in soil near Chernobyl isn’t decreasing nearly that fast. And scientists don’t know why.It stands to reason that at some point the Ukrainian government would like to be able to use that land again, but the scientists have calculated that what they call cesium’s “ecological half-life” — the time for half the cesium to disappear from the local environment — is between 180 and 320 years.

“Normally you’d say that every 30 years, it’s half as bad as it was. But it’s not,” said Tim Jannik, nuclear scientist at Savannah River National Laboratory and a collaborator on the work. “It’s going to be longer before they repopulate the area.”

A d v e r t i s e m e n t

The news may not bode well for Fukushima, although the reasons for the longevity of radioactive particles at Chernobyl is still a mystery.

Of course, some radioactive elements emitted by nuclear accidents – such as plutonium – can cause harm for thousands of years. As I noted in March:

Plutonium stays radioactive for a long time. Pu-238 has an 88-year half-life, Pu-239 has a 24,000-year half-life, and Pu-240 has a 6,500-year half life.

So plutonium might be heavier than other radioactive materials, but it is not so heavy that it can’t travel hundreds of miles in the right circumstances.

But cesium is much lighter, and can travel much further. And Chernobyl and Fukushima put out much higher quantities of cesium than plutonium (even with the explosions at Fukushima, which spewed plutonium over the surrounding area; and see this).